I'll assume that you don't have a humidor, or the cigars would not have dried out in the first place. Basically, you should do what has already been said. If you don't have a humidor, use a piece of wet sponge in a tupperware, just put something between them so the cigars don't actually touch the wet sponge. Start with the sponge barely damp. Do that for a week or two, then add a little more water to the sponge and do it again. Repeat until cigars have attained the desired humidity level.
The important thing is not to start with a sponge that is too wet. If the air in your home made "humidor" is too damp, the tobacco will absorb moisture too rapidly. This can cause the cigar to bulge and/or actually split.
Be patient. Good Cuban Cohibas are worth wating for.
